(1) Technical Field
The present invention relates to the fields of communications systems and computer networks and, in particular, to satellite networks, Direct-Broadcast-Service (DBS) broadcasting architectures, DBS uplink terminals, and DBS receive only subscriber ground terminals. More specifically, but without limitation thereto, the present invention pertains to a communication system and method that allows a transmitter segment (operator at uplink segment) to dynamically combine power from plurality of propagation channels (transponders) in order to improve power levels of signals being transmitted, without affecting the receiver segment (downlink segment) and the propagation segment (space segment), and without modifying the configuration of the propagation apparatus (satellite).
(2) Description of Related Art
Current direct-broadcast-service (DBS) satellite networks deliver many television (TV) programs over coverage areas via dedicated broadcasting satellites in geostationary orbits. DBS refers to satellite TV systems in which the subscribers, or end users, receive signals directly from geostationary satellites. A DBS subscriber installation consists of a dish antenna with a diameter between 50 to 90 centimeters, a conventional TV set, a signal converter placed next to the TV set (the set-top box), and a length of coaxial cable between the dish and the converter. Generally, the dish antenna intercepts the microwave signals transmitted directly from the satellite and the converter produces output signals that can be viewed on the TV receiver.
At the present time, the geostationary satellite orbit is the style most widely used for broadcasting, where the satellite is in an equatorial orbit and appears to be at a fixed point in the sky relative to an observer on the earth. The trend in the industry is to traditionally use the satellite in the “bent pipe” mode, where, as the term suggests, the satellite acts like a slingshot to redirect the incoming signal to different locations on earth. As a result, video coverage of an event at one place on the globe can be sent up to a satellite and redistributed (broadcast) over large areas of the populated world in the form of clear television pictures.
Generally, the signals are broadcast in digital format at microwave frequencies above 1010 Hertz (upper portion of the microwave Ku frequency band). As a result, the downlink, from satellite to earth, operates at frequencies between 12.2 Gigahertz (GHz) and 12.7 GHz. Accordingly, geo-satellite based direct TV broadcasting systems features high power Ku-satellites (transmitting at microwave frequencies above 10 GHz) and receiving-only ground terminals with small dishes. These satellite systems are very attractive for satisfying the wide area of coverage and the point-to-multipoint nature required for broadcasting.
Currently, operators over North America for full continental United States coverage utilize a group of multiple high-power or medium power satellites. These satellites fall into the category of either Broadcasting Satellite Service (BSS) or Fixed Satellite Service (FSS). Each satellite has many transponders, analogous to channels on a television receiver except that each transponder is capable of carrying many television signals simultaneously. These satellites, with maximum angular separations less than 25° in the geostationary arc, form a mini-constellation that can be simultaneously viewed by small, fixed, and round DBS antennas.
Perhaps, the two most important and most limiting assets of broadcasting satellites are the total available “satellite bandwidth” and “radiated power.” Although the information carrying capacity of satellites has been expanding steadily over the years since its inception, the available satellite bandwidth is still very small compared to the optical fiber bandwidth capabilities. This is particularly critical for the case of video transmission or high-speed data throughput, where there are severe limitations affecting the large bandwidth required by these transmissions. Progress in digital compression techniques is gradually reducing the bandwidth needed for video transmission. However, full-motion video still requires several Megabits per second.
Regarding the radiated power requirements of satellite communication systems, the radiated power levels and coverage antenna gains of broadcasting satellites dictate and limit the size and availability of subscriber terminals. As the technology moved forward in the last two decades, the available power for communications payloads on satellites increased from less than 100 watts (W) to over twenty kilowatts (20 kW).
Usually, satellite designs are initially optimized and balanced on both satellite bandwidth frequency and power assets for a given mission requirement, wherein it is considered to be a good practice to have both assets equally balanced, such as not to allow one of the two assets to reserve more space than the other. However, as time passes by, the mission requirement may change in time in a highly dynamic business environment. Therefore, the initial designs with balanced satellite assets may become non-optimal, as time passes by, and excessive space frequency and/or excessive power assets may become available for other applications at some points in time. As such, there is a need for a dynamic communication system that will take advantage of these free excessive power satellite assets dynamically available at some points in time to be utilized for other applications.
For the foregoing reasons, there is a great need in satellite communications for a system that allows an operator to dynamically allocate any existing available excess satellite radiated power to various programs (signals being transmitted) via multiple transponders in a satellite, or among multiple satellites, in order to improve the power levels of the various programs (signals being transmitted). Furthermore, there is a need for the dynamic power allocation to be controlled by the uplink segment (terminals or transmitter segment) without affecting the user-end of downlink segment (receiver segment) and the space segment (propagation segment), and without modifying the satellite configuration. In addition, for the dynamic power allocation to be successful, the receiving-only terminals must “coherently combine” the radiated power from the various transponders in order to enhance different broadcasting programs.
An embodiment of the present invention involves a dynamic improvement of radiated power over coverage areas by utilizing additional transponders on a satellite or from different satellites that are not being utilized at their full capacity and that have excessive (unused) radiated power available to be utilized, where the effective dynamic power allocations are utilized and implemented through the ground segment (transmitter segment or uplink segment) only, without affecting the space segment (propagation segment) configuration at all.
In addition to applications in satellite communications, there is a great need in communication systems in general to allow a user or an automated transmission system (transmitter segment) to dynamically allocate any existing available excess radiated power from propagation channels (in the propagation segment) to various applications, in order to improve power levels of transmitted signals and without affecting the receiver segment and the propagation segment (transmission medium, propagation apparatus, and propagation channels) of the communication system, and without modifying the configuration (infrastructure) of the propagation apparatus and propagation channels.
Some non-limiting and non-exhaustive examples of such communications systems (needing to dynamically allocate existing excess power available from propagation channels in order to improve power levels of transmitted signals without affecting the receiver segment and the propagation segment) are: wireless communication systems, fiber optical communication systems, wire communication systems, radio frequency communication systems, satellite communication systems, sonar communication systems, radar communication systems, laser communication systems, internet communication systems, communication systems between a vehicle and a satellite, communication systems between a least two vehicles, internal vehicle communication systems between the various operating subsystems within a vehicle, and any communication systems resulting from a combination of at least two of these communication systems therein.
The following references are presented for further background information:    [1] D. Chang, W. Mayfield, J. Novak III, and F. Taormina, “Phased Array Terminal for Equatorial Satellite Constellations,” U.S. Pat. No. 7,339,520, Mar. 4, 2008; and    [2] D. Chang, W. Lim, and M. Chang, “Multiple Dynamic Connectivity for Satellite Communications Systems,” U.S. Pat. No. 7,068,616, Jun. 27, 2006.